1. Field of the Invention
The present invention relates to a functional product, particularly to a functional product excellent in durability and appearance.
2. Discussion of Background
Conventionally, a Low-E glass (low emissivity glass), or a heat ray shielding glass (normally called a heat ray reflecting glass) wherein a multi-layer film is formed on a glass substrate having a large area by the magnetron sputtering method, has been employed. Since the glass employed in construction is excellent in energy conservation effect and design performance, it has considerably been prevailing in recent years.
As a use of the low emissivity glass which requires high durability, a window glass for an automobile is pointed out. In case of the window glass for an automobile, in recent years, the glass area in use has been increasing. For maintaining and promoting the comfort within an automobile, the low emissivity glass is beginning to be in use. In an automobile, it is required that the transmittance thereof is high and the reflection factor thereof is low in view of safety.
Especially, in an automobile, it is obligated by law that the visible light transmittance is not smaller than 70%. Furthermore, with respect to a reflection color thereof, a color tone caused by interference is not preferred and it is necessary to have an appearance as neutral as possible (an appearance similar to a normal uncoated glass).
The Low-E glass made by a sputtering method, is normally composed of three layers of an oxide film/a silver film/an oxide film. Since this type of Low-E glass employing silver, has a problem in durability, it cannot be employed in a single plate glass, and is used in a form of double glazing or laminated glass. For a windshield glass and a rear glass of an automobile, a low emissivity glass coated with a three-layer film composed of zinc oxide film/silver film/zinc oxide film made by a sputtering method on the side of a surface thereof for adhesion to form a laminated glass, is reduced into practice.
In the low emissivity glass of a single plate made by a sputtering method, a multi-layer film having two or three layers is formed by combining one layer selected from a metal film or a nitride film, and an oxide film or oxide films of tin oxide or titanium oxide. A reflection color tone generated by the necessary transmittance and optical interference is realized by pertinently controlling the film thickness. The low emissivity shielding glass having a high transmittance and a low reflection factor can be obtained by composing three layers of an oxide film/a nitride film/an oxide film, selecting the film material and controlling the film thicknesses. However, in case of a conventional film material, the function is not sufficient for the use of an automobile wherein high durability is necessary. Furthermore, since the conventional film material shows a reflection color generated by the optical interference, an improvement is required for the use of an automobile wherein a neutral color tone is necessary.
On the other hand, in case of a low emissivity glass in a single plate form, coated with an oxide film such as a titanium oxide film utilizing thermal decomposition, or a Low-E glass coated with an electrically conductive tin oxide, the reflection factor thereof is comparatively high and the durability thereof is not sufficient, which is not suitable for a low emissivity glass for the use of a door glass of an automobile.
A tempered single plate glass is employed for the door glass of an automobile in view of the strength. Therefore, the low emissivity film for that purpose requires high durability and a neutral color tone. A low emissivity film made by titanium nitride or the like coated with a composite oxide film as a protective film containing at least one selected from the group consisted of silicon and boron, and zirconium having high durability, is reduced to practice for that usage. This single plate low emission glass is excellent in durability and color tone. However, it is desirable to further promote the heat ray shielding function.
On the other hand, in case of a low emissivity glass composed of three layers wherein a low emissivity film made by titanium nitride or the like, is sandwiched by composite oxide films containing at least one selected from the group consisted of silicon and boron, and zirconium, having a high durability, it is possible to obtain the heat ray shielding film having a neutral color tone and excellent in heat ray shielding function, by controlling the content of silicon or boron and optimizing the refractive index. However, in case of the composite oxide film containing at least one selected from the group of silicon and boron, the film forming rate is low, the productivity is poor and a sintering hot press should be employed at elevated temperature to make a sputtering target, which increases the material cost. This was the hazard for the reduction into practice.
On the other hand, in case of a low emissivity glass for construction, there is no restriction of the neutral color as in the use for an automobile, and the specification thereof concerning the durability is rather alleviated. However, in the conventional low emissivity glass, the mechanical strength of the film is insufficient and the film is apt to be scratched. The scratch is often and mainly caused by carelessness in handling thereof. It is possible that the scratch is caused at every occasion including the production, the transportation, in construction of a building and in cleaning a window glass. The scratch in production gives rise to lowering of yield of product. The scratch in transportation, construction and cleaning thereof gives rise to claims for products.
To solve such a problem, it is considered to overcoat a metal oxide film which is hard, having a low coefficient of friction of surface, on the film of the conventional product. The overcoating material should be provided with a low coefficient of friction of surface and small refractive index to minimize the change of the color tone by the overcoating. Conventionally, as such a material, a composite oxide film is known which contains at least one selected from the group consisted of silicon and boron, and zirconium. However, as stated above, this material has drawbacks wherein "arcing" is apt to be generated in forming film, the film forming rate is low and the material cost is expensive.